Glad you got it working, sounds to me like it was a path issue but at least it's now working. No you don't need to uncheck everything when importing, as @lordmonkus and @DOS76 said that is just the default when actually importing, it can be changed anytime. As for the neo geo its very simple, just add the platform name and look at all the other cores above it in the associated platform list, they are all the same except for the actual name of the specific core. So just copy another line but replace the core name with the core you want to use.